The present invention relates generally to motor vehicle wheel end components. More particularly, the present invention relates to a brake assembly having a unique configuration and manufacturing process for reducing lateral run-out and a unique apparatus for machining the outer braking surfaces of a brake rotor.
Most motor vehicles today include disc brake systems for the front axle wheel assemblies and many further include disc brakes at the rear axle position. The disc brake rotor is a circular metal disc having opposed braking surfaces that are clamped by brake pads carried by a brake caliper to exert a braking effect. The wheel hub typically incorporates an anti-friction wheel bearing assembly in which one race of the bearing is coupled to the vehicle suspension and the other rotationally mounts the wheel hub, the brake rotor and wheel. Ordinarily, the rotating components of the rotor and hub assembly are manufactured separately and assembled together. This enables the brake rotor to be serviced and replaced if necessary during use. Moreover, the desired material characteristics for a brake rotor and the hub components are different. Although efforts to integrate these components have been proposed, such an approach has not found widespread acceptance.
In order to enhance performance of the braking system, it is desired to carefully and accurately control the dimensional characteristics of the rotor braking surfaces as the rotor rotates. The thickness variation of the disc and the lateral run-out or lateral deflection of the surfaces as they rotate need to be held to minimum tolerances. However, manufacturers have faced difficulties in achieving enhanced control over these tolerances due to the influence of several factors.
Most efforts to date have focused on decreasing run-out by controlling the dimensional characteristics of the rotor and therefore the relationship of the rotor surface to the wheel hub flange or surface. However, despite the fact that the tolerances and dimensional characteristics of the rotors have improved, performance and run-out problems still exist. These run-out problems are due in large part to other components of the wheel end assembly, including the bearing/hub assembly, which is comprised of a wheel hub and a bearing or the knuckle/hub assembly, which is comprised of a knuckle, a wheel hub, and a bearing.
One factor that contributes to this run-out is the stack-up of the individual components in a rotor/knuckle/hub assembly, i.e., their combined tolerances. While the tolerances of each part can be reduced when they are separately machined, when the parts are assembled, the combined tolerances stack up, causing run-out that is still relatively significant. Another factor that contributes to stack-up is any variation in the turning processes that are used to machine the wheel hub flange surface or the rotor surface, when the wheel hub and the rotor are individually machined, in an effort to make them flat. Further, the installation and press condition of the wheel bolts, the assembly process of the rotor/knuckle/hub assembly, and improperly pre-loaded bearings, can all cause misalignment of the rotor surface with respect to the brake pads and thus cause unacceptable run-out. This run-out can cause premature failure of the brake lining due to uneven wear which requires premature replacement of the brake lining at an increased expense. Further, problems due to run-out include, brake judder, steering wheel xe2x80x9cnibblexe2x80x9d and pedal pulses felt by the user, and warped rotors which result in brake noise and uneven stopping.
Presently available manufacturing methods and designs of rotors and knuckle hub assemblies to which the rotors are attached limit the accuracy to which lateral run-out of braking surfaces can be controlled. These methods and designs are also insufficient to solve the problems associated with run-out, as discussed above. Current methods typically involve finishing the rotor and the hub individually and then assembling the machined parts to form a completed brake rotor assembly. These methods, however, do not solve the run-out problems due to the factors discussed above, including stack-up tolerances, turning process variations, and wheel bolt and bearing installations.
Other options have been considered in an effort to solve the run-out problem, but they also all suffer from a variety of disadvantages. One contemplated option for reducing run-out is to separately decrease the run-out of each individual component, by decreasing their respective tolerances during manufacture and then assembling the components. The xe2x80x9cstack upxe2x80x9d of tolerance variations related to such an approach is still significant and provides only limited system improvement at an increased manufacturing cost. Another contemplated option includes tightening the press-fit tolerance variation between the knuckle, the wheel hub, and the bearing. This, however, significantly increases the difficulty in the assembly process as well as increases the manufacturing cost. Further, this option does not provide the desired reduction in system run-out.
It would therefore be advantageous to design a brake assembly for a motor vehicle that decreases system run-out without significantly increasing the manufacturing cost of the assembly or increasing the manufacturing difficulty.
It is therefore an object of the present invention to provide a brake assembly and a method for manufacturing same that provides reduced brake rotor lateral run-out.
It is a further object of the present invention to provide a brake corner assembly and a method for manufacturing same that results in a brake configuration which minimizes brake noise and uneven stopping.
It is still a further object of the present invention to provide a brake assembly and method for manufacturing same that results in a brake configuration which minimizes uneven brake lining wear and thus the need for frequent lining replacements.
It is a related object of the present invention to provide a brake assembly and a method for manufacturing same that results in a brake configuration which increases the life of vehicle brake linings.
It is yet another object of the present invention to provide a brake assembly and a method for manufacturing same that results in a brake configuration which provides improved performance at relatively lower cost.
It is yet a further object of the present invention to provide a tool to allow for the machining of a brake assembly to provide decreased lateral run-out on the outboard and inboard brake rotor faces.
In accordance with the objects of the present invention a brake assembly for a motor vehicle is provided. The brake assembly includes a knuckle having a plurality of apertures formed therein for attachment of the knuckle to a vehicle. The knuckle also includes a bearing retention portion. The knuckle bearing retention portion is in communication with a bearing through press-fitting. The bearing in turn is in rotational communication with a wheel hub. The wheel hub includes a neck portion that is pressed into the bearing, and a flange, having a flange face. The flange face has a plurality of bolt holes formed therein with each of the plurality of bolt holes receiving a wheel bolt passed therethrough. The flange face has a brake rotor secured thereto, which is finished such that it is parallel to the caliper mounting features, and wherein the brake rotor has minimal run out with respect to the bearing axis of rotation.
In accordance with another object of the present invention, a method for forming a knuckle/hub assembly having reduced run-out is provided. The method includes providing a knuckle having a generally circular bore formed therein. The generally circular knuckle bore has a bearing press-fit therein. A wheel hub having a neck portion and a flange portion with a flange face is provided. The flange face has a plurality of wheel bolts press-fit into bolt holes formed therein. The neck portion of the wheel hub is then journaled into the bearing such that the wheel hub can rotate with respect to the knuckle. A brake rotor is then secured to the wheel hub by locating it over the wheel bolts. Once the brake rotor is assembled to the wheel hub, the brake rotor surfaces are then final finished such that they are co-planar and parallel with respect to the caliper ears or pads.
In accordance with another object of the present invention, an assembly for holding a brake assembly while it is final finished is provided. The assembly includes a standard lathe machine with a fixture for clamping and locating the knuckle/hub assembly. The fixture applies a clamping force to the wheel hub and the inner race of the bearing to generate a pre-load on the bearing. The fixture also holds the knuckle in place so that the wheel hub may be rotated. Thereafter, the inner surface of the rotor is final finished so that it is flat and planar so as to provide minimal run-out when measured back to the brake assembly""s axis of rotation.